The present invention relates to a gas analyzer apparatus, and more particularly, to a flue gas analyzer apparatus for detecting and analyzing a predetermined chemical component contained in flue gas that flows through a flue.
To protect the global environment, flue gases emitted from combustion devices, such as internal combustion engines and combustion furnaces, are required to reduce their concentrations of nitrogen oxides. To satisfy this requirement, many flue gas analyzer apparatuses have been developed for detecting and analyzing nitrogen oxides contained in flue gases. The analysis results of a flue gas analyzer apparatus are reflected in combustion control for internal combustion engines and combustion furnaces to reduce concentrations of nitrogen oxides in their flue gases.
Known flue gas analyzer apparatuses include-direct-insertion type and gas-induction type flue gas analyzer apparatuses. A direct-insertion type flue gas analyzer apparatus is inserted in a flue at a measurement point to analyze the flue gas at that measurement point (refer to Japanese Laid-Open Patent Publication No. 63-58152). A gas-induction type flue gas analyzer apparatus induces flue gas sampled at a sampling point in a flue to a position distant from the sampling point and analyzes the flue gas at the distant position (refer to Japanese Examined Utility Model Publication No. 61-13964).
A direct-insertion type flue gas analyzer apparatus includes a probe for sampling the flue gas that flows in the flue. The probe is cylindrical and has a flange. The probe is inserted through a hole that is formed in an exhaust pipe (flue) of a combustion furnace etc. and is fixed to the exhaust pipe by means of its flange. A porous metal-sintered filter is arranged on a distal portion of the probe. A gas sensor is arranged in the probe at a position adjacent to the metal-sintered filter. A known solid electrolyte gas sensor uses a solid electrolyte formed from a ceramic such as zirconia. The flue gas that flows in the exhaust pipe is drawn into the probe through the metal-sintered filter. The gas sensor then performs detections on the gas in the probe. A terminal unit is arranged at a basal portion of the gas sensor. The terminal unit is electrically connected to an external control unit by lead wires.
A gas-induction type flue gas analyzer apparatus includes a gas sampling tube. The gas sampling tube includes a distal portion having a gas inlet and a basal portion having a gas outlet. The gas sampling tube is bypass-connected to an exhaust pipe. The distal portion of the gas sampling tube is arranged in the exhaust pipe. A solid electrolyte gas sensor is arranged in the gas sampling tube. The dynamic pressure of the gas that flows in the exhaust pipe causes gas to flow into the inlet of the gas sampling tube. The gas then comes into contact with the solid electrolyte gas sensor and then flows out of the outlet of the gas sampling tube so as to return to the exhaust pipe. A detection signal of the gas sensor is transmitted to an external meter through lead wires drawn out of a terminal unit.
In such conventional flue gas analyzer apparatuses, the distal portion of the probe or the gas sampling tube is arranged in or near the center of the exhaust pipe. This arrangement enables the flue gas analysis to be conducted without being affected by an eddy that is often generated at the inner surface of the exhaust pipe. The length of the portion of the probe or gas sampling tube inserted into the exhaust pipe is determined in accordance with the diameter of the exhaust pipe. Thus, the insertion length of the probe or the gas sampling tube in the exhaust pipe increases as the diameter of the exhaust pipe increases and decreases as the diameter of the exhaust pipe decreases. The gas-induction type flue gas analyzer apparatus simply requires the insertion length of the gas sampling tube in the exhaust pipe to be adjusted but does not require the position of the gas sensor to be changed. However, depending on the diameter of the exhaust pipe, the direct-insertion type flue gas analyzer apparatus, in which the gas sensor is arranged in the distal portion of the probe, may require the entire gas sensor, which includes its basal portion in which the terminal unit is arranged, to be arranged in the exhaust pipe.
To keep the lead wires drawn out from the terminal unit in a bundled state, a lead wire bundling cap is attached to the basal portion of the gas sensor. The lead wire bundling cap is a circular plate having a plurality of holes. The lead wire bundling cap is made, for example, from an elastic rubber material. The lead wires are drawn through the holes of the lead wire bundling cap. When the gas sensor is used in a high temperature environment, the lead wire bundling cap is easily damaged by heat.
To prevent heat damage to the lead wire bundling cap, materials having high heat resistance (e.g., ceramics or a metal material such as platinum) may be used to form the lead wire bundling cap. However, materials having high heat resistance are expensive. The use of such a material increases the costs of the components used in the flue gas analyzer apparatus. The flue gas analyzer apparatus is required to reduce heat damage of the basal portion of the gas sensor without increasing the component costs.